(a) Field of the Invention
The present invention relates to an electronic musical instrument, and more particularly it pertains to an electronic musical instrument of the waveshape memory type wherein waveshapes are successively read out from the memories and then converted to musical tones.
(b) Description of the Prior Art
In conventional electronic musical instruments of the so-called waveshape memory type, a certain waveshape is previously stored in a storage means and is repetitively read out, in response to key depression, at a rate associated with the depressed key to produce a corresponding musical tone.
A typical example of overall arrangement of such a conventional electronic musical instrument is shown in block in FIG. 1. In this Figure, a keyboard circuit 2 is provided for selecting a musical tone to be produced in response to the operation of the keyboard arrangement (not shown) of the instrument. When a key in the keyboard arrangement is depressed, the keyboard circuit 2 generates the logical "1" signal only on an output line assigned to the depressed key to instruct the selected key number to a frequency information memory 4. Also, a key-on signal KON is delivered from the keyboard circuit 2 upon depression of any one of keys and is kept generated as long as the key is kept depressed. The keyboard circuit 2 is further equipped with means for selecting one key, in preference to others, among a plurality of keys depressed at a time and thus specifying a single key to be evaluated. As such preference key selection means, there may be employed such circuits as those disclosed in U.S. Pat. No. 3,981,217 issued on Sept. 21, 1976 and assigned to the same assignee as the present application.
Output lines of the keyboard circuit 2 are fed to the address input of the frequency information memory 4 in which is stored the frequency information corresponding to each key. Thus, when a key is selected and depressed, the frequency information memory 4 is accessed with an address given by the output line of the keyboard circuit 2, and a frequency information corresponding to the selected key is read out from the memory 4. The read-out frequency information is successively added to the content of the cumulative adder 6 at each arrival of a clock pulse .phi. in the adder with a modulus. The temporary content of the adder 6 is successively transferred to the address input of a waveshape memory 10. In the waveshape memory 10, there has been previously stored a waveshape in a digital representation, for instance. More particularly, the amplitudes for a plurality of sample points of a composite waveshape including a fundamental component as well as many harmonic components are stored in individual address locations of the memory 10. Accordingly, the waveshape memory 10 is repetitively accessed with the contents of the adder 6, i.e. the addresses and the amplitudes of the stored waveshape are successively read out. As will be seen from the previous explanation, the incrementing or decrementing rate of content of the adder 6 is dependent upon a particular key depressed. As a result, there will be obtained from the waveshape memory 10 a waveshape at a repetition period, i.e. a fundamental frequency corresponding to the depressed key.
An envelope generator 15 and a multiplier 12 are provided for imparting a required envelope characteristic to the waveshape generated from the waveshape memory 10. The envelope generator 15 is designed to operate so that when initiated by the key-on signal KON, it generates an envelope waveshape. The envelope waveshape may be classified roughly into two types: a percussive waveshape as shown in FIG. 2A and a sustained waveshape as illustrated in FIG. 2B. The envelope generator is preferably designed so that either one of these two types of envelope waveshapes can be selected by means of a musical tone selection switch on the panel board of the instrument.
The waveshape which is read out from the waveshape memory 10 is fed to the multiplier 12 and multiplied with the envelope waveshape generated by the envelope generator 15 in the multiplier. Thus, envelope-imparted waveshape is obtained in the multiplier 12, which, in turn, is inputted to a sound system 14 to be converted into a musical tone. The sound system 14 essentially consists of an audio amplifier and a loud speaker, and may also include a digital-analog converter if the waveshape in the memory 10 is in a digital representation.
As explained above, with the conventional musical instrument, it is possible to obtain a musical tone which is provided with an amplitude transient characteristic, i.e. an envelope characteristic. However, the musical tone produced by the conventional instrument remains unchanged in tone color during the entire period of the generation thereof, because a single kind of waveshape retrieved from the waveshape memory is used for the generation of the musical tone. In contrast thereto, a sound pronounced by a natural musical instrument is such that its tone color, i.e. the frequency spectrum of the sound, will continuously change during the generation with the lapse of time. Accordingly, the musical tone produced by the conventional instrument is liable to lack richness in tone color and to be just monotonous.